Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
STUDY OF NOVEL PVD COATINGS FOR REDUCING CUTTING TOOLS DETERIORATION IN
THE MACHINING OF TITAIUM ALLOYS Cadena De la Peña Natalia Lissette, Cué Sampedro Soberanis Rodrigo, Siller Carrillo Héctor R.
Tecnológico de Monterrey, Campus Monterrey
Eugenio Garza Sada 2501, 64849 Monterrey, N.L. México
Teléfono: +52 (81) 83582000 Ext. 5430;
[email protected], [email protected], [email protected]
RESUMEN
En este artículo se muestran resultados de pruebas
hechas en herramientas de carburo de tungsteno
recubiertas para aplicaciones industriales. En esta
investigación se estudiaron películas delgadas
hechas principalmente de nitruros, óxidos y
nitróxidos nanocompuestos, mostrando trabajo
experimental en deposición y caracterización. Se
realizaron cuatro tipos de análisis en los
recubrimientos: Dispersión de rayos X para
determinar su composición, difracción de rayos X
para determinar estructuras cristalinas, pruebas
pin-on-disk para estudios tribológicos que
determinan coeficientes de fricción y resistencia al
desgaste y finalmente se hicieron pruebas de
maquinabilidad para evaluar cuestiones clave del
rendimiento de herramientas de corte a
temperaturas elevadas. Se demostró que a mayor
dureza y menor coeficiente de fricción, se presenta
mayor rendimiento en las pruebas de maquinado.
ABSTRACT
This article shows results of tests made on coated
tungsten carbide tools for industrial applications.
Thin films mainly made out of nitrides, oxides and
nano-composites nitroxides were studied in this
research, showing experimental work in
deposition and characterization. Four types of
analysis were performed on the coatings: X-ray
Energy Dispersion for composition determination,
X-ray diffraction to determine crystalline
structure, pin-on-disk tests for tribological study
to determine friction coefficient and wear
resistance and finally machinability tests were
performed to evaluate key issues of cutting tools
in high end cutting performance at elevated
temperatures. It was demonstrated that coatings
with higher hardness and lower friction coefficient
are more efficient in machinability tests.
NOMENCLATURE
ap, Axial depth of cut
ae, Radial depth of cut
µ, Friction coefficient
Fz, Feed per tooth
Vb, Flank wear
Vc, Cutting speed
INTRODUCTION
Depositions of nanoscale multilayered coatings
are extensively investigated and developed due to
their pronounced strength enhancement, high
toughness and excellent wear resistance. In the
study of Kao et. al [1], TiAlN/CrSiN coatings
multilayered thin films were synthesized and
characterized by X-ray diffraction and dispersion,
examined by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM). The
surface roughness was explored by atomic force
microscopy (AFM). Also, micro Vickers and pin-
on-disk tests were used to evaluate hardness.
Certain changes in deposition, constitution,
structure and composition of coatings materials
make them more suitable for industrial
applications. Main applications of these
multilayered coatings are in cutting tools,
prosthesis implants, mould and die, etc.
Machining at considerably high cutting speeds is
known as High-speed machining (HSM) and it is
a very accurate technology in manufacturing
dimensionally precise parts [2]. However,
ISBN 978-607-95309-6-9 Página | 978
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
working with HSM implies a great temperature
rise in materials which is the major concern in the
selection of process parameters. This high cutting
temperature generated reduces the tool life and its
quality. A wide variety of cutting fluids are used
to eliminate the effects of heat and friction [3] but
these may create environmental problems. To
avoid pollution and reduce processing cost, new
manufacturing dry machining technologies are
being performed and because of this, Physical
Vapor Deposition (PVD) is used to coat cutting
tools. PVD coating increases the life of tools and
also makes them more productive because coated
tools can be run faster, reducing the time of
production. In the work of Kalss et. al [4], the
influence of key properties of nitride coatings in
relation to metal cutting is discussed.
The present research focused mainly on the
development of new nano-structured coatings
based on nitrides, oxides, nitroxides and nano-
composites. The coatings were developed with
different structural properties based on two main
compounds: Titanium-Aluminum-Nitrogen
(TiAlN) and Aluminum-Chromium-Nitrogen
(AlCrN). TiAlN has been widely applied for
coating tools to prolong their lifetime and
performance [5]. AlCrN is a relatively new ternary
nitride with high amounts of aluminum that has
shown excellent properties under high
temperatures [6]. These two types of coatings
were tested and compared for tribological,
morphological and structural behavior.
As a hypothesis, it was well known that TiAlN
had a better wear performance, but more
experimental work was necessary to compare new
commercial coatings.
EXPERIMENTAL WORK
For each of the compounds of AlCrN and TiAlN
four types of coatings were deposited: Mono-
layer, Heat-treated mono-layer, Bi-layer and
Multilayer. All coatings were deposited on
tungsten carbide substrates Kennametal Grade
2210 through physical vapor deposition by
cathodic arc (arc-PVD) using a system Bias &
Cathodic Arc Evaporation of the brand Oerlikon-
Balzers. For the deposition of the coatings, targets
of Al70Cr30 and Al67Ti33 alloys were used (both
in weight %) in a controlled nitrogen atmosphere.
The deposition time for each coating was adjusted
to obtain a predetermined thickness: 4 μm for
AlCrN, and 2 μm for TiAlN.
The morphological characterization of the cross
section of the coatings was performed by two
scanning electron microscopes: Nova NanoSEM
200 and FEI Company JEOL JSM-6700F. The
elemental chemical analysis was done using an
Energy Dispersive X-ray detector (EDX) of the
brand Oxford with a detection limit of 0.1% wt.
The crystalline structure was characterized by X-
ray diffraction (GI-XRD PANalytical X'Pert PRO
MRD) with grazing incidence from 20° to 80° and
angle of incidence of 0.5°. Hardness tests were
conducted by means of a nanoidentator
MicroVickers Clemex MMT-X7 equipped with a
pyramidal diamond tip Berckovitch applying 1
kgf during 10 seconds. The wear tests were
performed on a tribometer Pin-On-Disk CSM-
Instruments with a load of 1 N for a period of
8000 s with a sapphire sphere.
Machinability tests were performed with an end
milling process in a Vertical Machining Center
Makino F3 three axis, with the following
parameters (Table 1). The machined material
consisted of a titanium alloy Ti6Al4V aerospace
grade.
Table 1.
Fixed milling parameters
Spindle (max) RPM 30000
Tool fixturing
HSK63
Feedrate (max) mm/min 20000
Tool diameter mm 12.7
Axial depth of cut, ap mm 5
Radial depth of cut, ae mm 0.6
Vc m/min 150
fz mm/tooth 0.06
Emulsion (refrigerant) 5%
EXPERIMENTAL RESULTS
For the AlCrN coatings an optimum thickness of 4
μm was selected for best performance of the tool.
ISBN 978-607-95309-6-9 Página | 979
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
All AlCrN depositions were made under nitrogen
atmosphere, to ensure the nitriding of the
compound. The deposition time of each coating
was varied due to the complexity of the
parameters involved. The deposition of AlCrN-M
and AlCrN-T coatings was carried out with the
Al70Cr30 target for 4 hours. For the AlCrN-BC
coating, the deposition was interrupted with the
intention of creating a bi-layer coating, using a
deposition time of 150 minutes for the first layer
and 90 minutes for the second. For the AlCrN-MC
coating alternated deposition in a sequence of 8
cycles of 30 minutes each. Table 2 shows the
main features of the AlCrN depositions.
Table 2
Main features of the AlCrN samples
Coating Main feature Thickness
(μm)
Composition ICSD Structure Planes (hkl)
AlCrN-M Mono-layer 4 Al 34.46%at
Cr 17.48%at N
48.04%at
CrN 01-074-
8390
Cubic (111)
AlN 01-077-
6808
Cubic (111) (200)
(220)
AlCrN-T Heat-treated mono-
layer
4 Al 32.31%at
Cr 27.85%at N
39.84%at
CrN 01-074-
8390
Cubic (111)
AlN 00-025-
1495
Cubic (100) (101)
AlCrN-
BC
Bi-layer 4 Al 30.30%at
Cr 19.39%at N
50.31%at
AlCr 01-074-
5156
Cubic (110) (200)
AlN 01-077-
6808
Cubic (111) (200)
(220)
AlCrN-
MC
Multilayer 4 Al 37.89%at
Cr 13.38%at N
48.73%at
CrN 01-074-
8390
Cubic (111)
AlN 00-025-
1495
Cubic (100) (101)
Table 3
Main features of the TiAlN samples
Coating Main feature Thickness
(μm)
Composition ICSD Structure Planes (hkl)
TiAlN-M Mono-layer 2 Ti 28.56%at
Al 20.93%at N
50.51%at
AlN2Ti 01-
071-5864
Cubic (110) (200)
WC 03-065-
8828
Hexagonal (001) (100)
(101)
TiAlN-T Heat-treated mono-
layer
2 Ti 27.72%at
Al 21.87%at N
50.41%at
AlN2Ti 01-
071-5864
Cubic (110) (200)
WC 03-065-
8828
Hexagonal (001) (100)
(101)
TiAlN-BC Bi-layer 2 Ti 40.33%at
Al 53.57%at N
47.13%at
AlN2Ti 01-
071-5864
Cubic (110) (200)
WC 03-065-
8828
Hexagonal (001) (100)
(101)
TiAlN-MC Multilayer 2 Ti 32.80%at
Al 49.50%at N
17.70%at
AlN 00-025-
1495
Cubic (100) (101)
AlN2Ti 01-
071-5864
Cubic (110) (200)
WC 03-065-
8828
Hexagonal (001) (100)
(101)
ISBN 978-607-95309-6-9 Página | 980
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
For the TiAlN compounds, an optimum thickness
of 2 μm was selected. As in the AlCrN coatings, a
nitrogen atmosphere was used and the deposition
time was varied. Table 3 shows the main features
of the TiAlN depositions.
Morphological results
Fig. 1 shows that the thickness of the coating
AlCrN-M is constant ≈ 3.8 μm and homogeneity
can be observed, indicating that the coating
composition is uniform. Fig. 2 shows the X-ray
fluorescence spectrum analysis of the AlCrN-M
coating giving a composition of Al 34.46%at, Cr
17.48%at, N 48.04%at. To improve the properties
of the AlCrN-T coating, it was deposited under
the same conditions as the AlCrN-M coating with
the only difference that a deposition temperature
of 500 °C was used. Fig. 3 shows the SEM image
of the AlCrN-T coating, it can be observed as in
the AlCrN-M coating that the film is
homogeneous. The composition of the AlCrN-T
coating resulted as Al 32.31%at, Cr 27.85%at, N
39.84%at, it has a considerable variation with
regard to the AlCrN-M coating (Fig. 2).
The AlCrN-BC coating consists of two thin films
of the same material. Fig. 4 shows the interface of
the two films. The first layer, adhered to the
substrate is homogeneous throughout its
thickness, but the second layer shows embedded
light spots in the film. The coating composition
obtained for the AlCrN-BC coating is Al
30.30%at, Cr 19.39%at, N 50.31%at.
The multilayer coating AlCrN-MC is shown in
Fig. 5. Separations of the layers along the film
thickness can be observed. The EDX analysis of
the AlCrN-MC coating indicates that the
composition is Al 37.89%at, Cr 13.38%at,
N48.73%at.
Fig. 1 SEM image of the AlCrN-M coating Fig. 2 EDX analysis of the AlCrN-M coating (Al
34.46%at Cr 17.48%at N 48.04%at)
ISBN 978-607-95309-6-9 Página | 981
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
To enhance the TiAlN-T coating properties it was
deposited under the same conditions than the
TiAlN-M coating with the only difference that a
deposition temperature of 600 °C was used. Fig. 6
is a SEM image of the TiAlN-T coating and it
shows that the film is homogenous. The
composition of the TiAlN-T coating is Ti
27.72%at, Al 21.87%at, N 50.41%at. This
composition does not have a considerable
variation with that of TiAlN-M. The SEM image
of the multilayered coating TiAlN-MC is shown
in Fig. 7. The separations of the layers are visible
along the film thickness.
Structural results
Fig. 8 shows the XRD diffractograms of the four
AlCrN coatings. The diffractogram of the tungsten
carbide substrate grade 2210 - Kennametal was
joined to the graph to show that the peaks are
Fig. 3 SEM image of the AlCrN-T coating Fig. 4 SEM image of the AlCrN-BC coating
Fig. 5 SEM image of the AlCrN-MC coating Fig. 6 SEM image of the TiAlN-T coating
Fig. 7 SEM image of the TiAlN-MC coating
ISBN 978-607-95309-6-9 Página | 982
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
specifically those of the coatings and not a
mixture of substrate and film.
The AlCrN-M coating shows two structures. One
is cubic CrN corresponding to the ICSD
crystallographic coordinate CrN 01-074-8390,
with a preferential peak at the plane (111). The
other is AlN 01-077-6808 (111) (200) (220). The
coating AlCrN-T has the same CrN cubic
structure than the AlCrN-M coating but with a
higher intensity, indicating crystal growth.
However, a structural transition is visible in the
compound with the structure corresponding to the
crystallographic coordinate 00-025-1495 with
preferential peaks (100) (101). This indicates that
the heat treatment allowed AlN to recrystallize
and CrN to increase it crystal size. The AlCrN-BC
coating shows two AlN structures corresponding
to the crystallographic coordinates 01-077-6808
with planes (111) (200) and (220) and a AlCr
structure corresponding to the crystallographic
coordinates 01-074-5156 with planes (110) and
(200). The AlN structure has the same phase than
the AlCrN-M coating but the AlCr structure is not
present in any other coating. This structure is
found mainly in the interface of the two layers.
The multilayer coating AlCrN-MC presents the
same phases as found in the coating AlCrN-T with
heat treatment, with the difference that the
intensity of the peaks is lower, indicating that the
crystal size of both structures is much lower.
Fig. 9 shows the diffractograms of the coatings
TiAlN-T and TiAlN-MC. The diffractograms of
the TiAlN coatings show peaks corresponding to
the tungsten carbide (WC) substrate. This is
mainly due to that the thickness is thinner than
AlCrN coatings. The TiAlN-M coating shows a
structure corresponding to its AlTi2 cubic
elements with the crystallographic coordinates 01-
071-5864. The multilayer TiAlN-MC coating
shows two main structures, AlN and AlN2Ti
corresponding to the crystallographic coordinates
00-025-1495 and 01-071-5864 respectively. The
TiAlN-MC coating has an AlN structure that is
not present in any other coating and it corresponds
to the crystallographic coordinate 00-025-1495.
This structure is found mainly in the interface of
the layers.
Fig. 8 Diffractograms of the four AlCrN coatings and substrate WC 2210.
ISBN 978-607-95309-6-9 Página | 983
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
Tribological results
In Fig. 10, the friction coefficient in function of
wear length is shown for the coatings AlCrN-T
(monolayer) and AlCrN-MC (multilayer). The
average friction coefficients of the monolayer and
multilayer coatings are 0.42 and 0.55 respectively.
Fig. 11, shows the friction coefficient of the
TiAlN-MC coating.
The hardness of the AlCrN and TiAlN coatings
are presented in Table 4.
Fig. 10 Friction coefficient of the AlCrN coatings. Fig 11 Friction coefficient of the TiAlN coatings.
Table 4
Hardness of the AlCrN and TiAlN coatings
Hardness
Vickers scale
AlCrN-T
(monolayer)
AlCrN-BC
(bilayer)
AlCrN-MC
(multilayer)
TiAlN-T TiAlN-BC TiAlN-MC
1 1870 1920 1724 1743 1736 1693
2 1898 1856 1942 1711 1781 1699
3 1912 1862 1724 1775 1775 1675
4 1762 2043 1794 1808 1808 1743
5 1755 1980 1681 1775 1724 1749
6 1736 2083 1730 1718 1768 1651
7 1821 2067 1794 1835 1801 1657
8 1828 2143 1743 1743 1821 1663
9 1870 2019 1814 1705 1808 1699
10 1781 1995 1693 1768 1891 1675
Average 1823.3 1996.8 1763.9 1758.1 1791.3 1690.4
0
0.2
0.4
0.6
0.8
1
1 10 100 1000 10000
Fric
tio
n c
oe
ffic
ien
t
T ime(s)
TiAlN-T
TiAlN-MC
Fig. 9 Diffractograms of the TiAlN coatings substrate WC 2210.
ISBN 978-607-95309-6-9 Página | 984
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
Machinability tests
Machinability tests were carried out with a control
limit of 300 microns of flank wear in the cutting
tool, according to the standrd ISO 8688-2. Fig. 12
shows the results of the machinability tests for a
cutting speed Vc of 150 m/min and a feed per
thoot of 0.06. Fig. 13 shows the flank wear at 5
meters of machined distance.
CONCLUSIONS
The four AlCrN coatings deposited showed
physical properties with a wide range of
applications in manufacture. The structural
analysis shows that the thermal treatment allows
recristalization and crystal growth, enhancing its
mecanical properties like hardness and wear
resistance. These characteristics make the coated
tools better for cutting aplications. Also, plastic
deformations make the tools better in performance
for stamping. For the TiAlN coatings, hardness
and plastic deformation reached maximum values
in the bi-layer coating (TiAlN-BC). Hardness
increases with two layers but decreases with
multiple layers.
The friction coefficient of the AlCrN coatings
measured in the pin on disk tests was lower than
that of the TiAlN coatings. It took around 60
cycles for the friction coefficient of TiAlN to
reach its maximum value of approximately 0.7,
while more than 2000 cycles were needed for the
AlCrN layer to reach a value of 0.55. The AlCrN
coatings presented better anti-wear properties with
a lower friction coefficient than the TiAlN
coatings. AlCrN coatings have greater potential in
tribological applications than TiAlN coatings
under similar conditions.
In the machinability tests with a cutting speed
(Vc) of 100 m/min, the family of TiAlN coatings
demonstrated higher wear resistance than the
AlCrN family coatings using a feed of 0.04 mm.
For more aggressive feed parameters, the
performance of the AlCrN coatings family is
improved. Using a Vc = 150 m /min the family of
TiAlN coatings have better wear resistance. This
result shows that this family of coatings is better
at higher cutting speeds but lower feed rates.
The best performance was obtained with the heat
treated coatings, resulting even better than that of
multilayered coatings. Specifically TiAlN-T
coatings demonstrated to be more suitable for
machining due to its low friction coefficient for
longer cycles and greater wear resistance in high
speed machining.
REFERENCES
[1] Kao Chien-Ming, Lee Jyh-Wei, Chen Hsien-
Wei, Chan Yu-Chen, Duh Jeng-Gong, Chen Shin-
0
50
100
150
200
250
300
0 10 20 30
flan
k w
ear
Vb
[µ
m]
Machined distance(m)
Vc 150 m/min - fz 0.06
TiAlN-T
AlCrN-T
TiAlN-MC
AlCrN-BC
TiAlN-M
TiAlN-BC
Fig. 12 Machinability test with a Vc of 150
m/min and a feed per tooth fz of 0.6
Fig. 13 Flank wear of the coatings at 5 meters
of machined distance
ISBN 978-607-95309-6-9 Página | 985
MEMORIAS DEL XVIII CONGRESO INTERNACIONAL ANUAL DE LA SOMIM
19 al 21 DE SEPTIEMBRE, 2012 SALAMANCA, GUANAJUATO, MÉXICO
Derechos Reservados © 2012, SOMIM
Pei. Microstructures and mechanical properties
evaluation of TiAlN/CrSiN multilayered thin
films with different bilayer periods. Surface &
Coatings Technology 205 (2010) 1438-1443.
[2] Rodrigues, Alessandro Roger et al. Surface
integrity analysis when milling ultrafine-grained
steels. Mat. Res. 2012, vol.15, n.1, pp. 125-130.
[3] Kuram E, Simsek B. T., Ozcelik B.,
Demirbas E., Askin S. Optimization of the
Cutting Fluids and Parameters Using Taguchi and
ANOVA in Milling. Proceedings of the World
Congress on Engineering 2010 Vol II. WCE 2010,
June 30 - July 2, 2010, London, U.K.
[4] Kalss W., Reiter A., Derflinger V., Gey C.,
Endrino J.L. Modern coatings in high
performance cutting applications. International
Journal of Refractory Metals & Hard Materials 24
(2006) 399–404.
[5] Cardoso Brandão Lincoln, Teixeira Coelho
Reginaldo, Roger Rodrigues Alessandro.
Experimental and theoretical study of workpiece
temperature when end milling hardened steels
using (TiAl)N-coated and PcBN-tipped tolos.
Journal of materials processing technology 199
(2008) 234–244.
[6] J.L. Mo, M.H. Zhu, B. Lei, Y.X. Leng, N.
Huang. Comparison of tribological behaviours of
AlCrN and TiAlN coatings—Deposited by
physical vapor deposition, Wear 263 (2007)
1423–1429.
ISBN 978-607-95309-6-9 Página | 986